The invention relates generally to automatic gain control, and more particularly to an automatic gain control system that automatically adjusts the gain of a plurality of incoming signals having varying amplitudes (e.g., return signals from a multiple wavelength laser LIDAR) to output signals having peak amplitudes that fall within a prescribed range regardless of the peak amplitude levels of the incoming signals.
The use of automatic gain control systems is prevalent in a variety of applications where it is necessary to boost or reduce a signal level so that the signal level falls within a range of amplitudes that can be handled by a data processor. Specifically, signal levels must be boosted if they are too low to be interpreted by the data processing electronics while signal levels must be reduced if they would saturate the data processing electronics.
One example of a system that produces signals having output levels that change constantly and rapidly is a multiple wavelength laser LIDAR system that can be used to detect a variety of airborne chemical and biological agents. Briefly, such LIDAR systems make use of a frequency agile laser to transmit sets of time-separated laser pulses of varying wavelength into the atmosphere. Laser returns at the varying wavelengths generated by the laser pulses are detected and analyzed to determine the presence and/or concentration of various chemical and biological agents. Each different wavelength is selected to detect a xe2x80x9ctargetxe2x80x9d chemical or biological agent having unique absorption and reflection characteristics relative to the specific wavelength.
The problems associated with analyzing the returns from such LIDAR systems are twofold. First, the amplitudes of the transmitted laser pulses will vary from wavelength-to-wavelength. Thus, everything else being equal, the laser returns will also vary in amplitude. Second, since the transmitted pulses will be absorbed/reflected differently depending on the xe2x80x9ctargetxe2x80x9d agent in the atmosphere, the signal amplitude of the laser returns can vary greatly. Thus, it is entirely possible that the amplitude of one laser return is too low for the detector/analyzer of the LIDAR system, while the amplitude of the next laser return is so great that it saturates the detector/analyzer of the LIDAR system.
Accordingly, it is an object of the present invention to provide a system for automatically adjusting the amplitude or level of a return signal received from an interrogating system that transmits sets of time-separated interrogating signals to generate corresponding sets of time-separated return signals.
Another object of the present invention is to provide an automatic gain control system that can be used with a multiple wavelength laser LIDAR system to adjust the signal level associated with each laser return.
Still another object of the present invention is to provide an automatic gain control system for a multiple wavelength laser LIDAR system that adjusts the signal level associated with each laser return to fall within a prescribed window of signal levels.
Yet another object of the present invention is to provide an automatic gain control system for a multiple wavelength laser LIDAR system that can select laser returns within a specified range window.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
The present invention is used in conjunction with an interrogating system (e.g., a multiple wavelength laser LIDAR system) that transmits sets of time-separated interrogating signals to generate sets of time-separated return signals. The present invention is a system for automatically adjusting a level of each of the return signals. A comparator defines a plurality of unique peak amplitudes and a corresponding plurality of unique binary words associated therewith. The comparator receives each return signal from an i-th set of the interrogating signals and outputs a binary word indicative of a peak amplitude achieved thereby. The binary word is one of the plurality of unique binary words. A first memory coupled to the comparator stores each binary word associated with each return signal""s peak amplitude from the i-th set. A second memory is coupled to the first memory and has each of a plurality of address locations defined by one of the plurality of unique binary words. Each address location in the second memory stores a unique gain value. An adjustable gain amplifier has a signal input for receiving each return signal and a gain adjustment input coupled to the second memory. One of the unique gain values associated with each return signal from the i-th set is supplied to the gain adjustment input to adjust the gain of the adjustable gain amplifier for corresponding ones of the return signals from an (i+1)-th set of the return signals.